Telephone-exchange system



A. E. LUNDELL. TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED DEC. 29, 1916. v

Patented Jan. 17, 1922.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED DEC.29, 1916.

Patented Jan. 17, 1922.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED DEC.29, 1916.

vPatented Jan. 17, 19,22.

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APPLICATION FILED DEC. 29,1916. 1,403,861 Patented Jan. 17, 1922.

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A. E. LUNDELL. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED DEC.29| 1915. l 1,403,861 Patented Jan. 17, 1922.

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UNITED STATES ,ATENT OFFICE.

ALBEN E. LUNDELL, OF NEW YORK, N. Y., ASSIGNOR T WESTERN ELECTRIC COM- PANY, INCORIPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed December 29, 1916.

To all whom t may concern.'

Be it known that I, ALBEN E. LUNDELL, a

citizen of the United States, residing at New York, in the county of Bronx and State of New York, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to electrical con trolling systems, and particularly to electrical controlling systems for automatic. or semi-automatic telephone exchanges.

In telephone exchange systems in which an impulse controlling device, such as a sender, controls the operation of selector switches by means of which connections may be established, it has been the practice to provide a plurality of sending units each composed of the sender proper and the means by which the number of effective operations of the sender may be determined. In order to obviate the necessity of providing one sending unit for each trunk leading to a selector, it has been proposed to provide automatically operating switching devices, such as cord iinders, sender selectors, etc., by means of which a sending unit may be selectively associated with any one of a plurality of trunks or link circuits leading to selector switches. In such systems a position or station from which the operation of the selector switches is controlled must be equipped with at least one sending unit, which may be associated by manual or autematic means with a trunk leading to the selector switch to be set.

ln order to do away with the necessity of' providing an impulse controlling device at each operators position in a semi-automatic telephone exchange, systems were designed to provide one constantly operating impulse controlling device for the whole exchange, and to connect in multiple each operators keyboard to the common controlling device. rEhe mentioned multiple connection of the keyboards renders this arrangement expensive.

It is the object of the present invention to reduce the cost of electrical controlling systems, applicable particularly to automatic and semi-automatic telephone exchanges by reducing and simplifying the im nilse controlling units provided for the control of selector switches.

In its broadest aspect, the present inven- Speccaton of Letters Patent.

Patented Jan. 17, 1922.

Serial No. 139,511.

tion may be dened as relating to an electrical controlling system in which a secondary controlling device such as a sender of the impulse sending or receiving type by which the setting of selectively operable switches may be controlled, is normally not associated with a primary controlling device by means of which its operation may be determined, means being provided for elicoting the association between the sender and the controlling device.

According to one feature of the invention, an impulse sending or receiving device having a normal position and a plurality of operating positions for controlling the setting of selector switches, may be variably operated in accordance with the adjustment of a controlling device, such as a keyooard, normally disassociated therefrom.

According to another feature of' the invention, any one of a plurality of variably operable impulse sending or receiving devices by which the setting of the selector switches is controlled, may be variably adf justed for operation by any one of a plurality of controlling devices selectively associablc therewith. By means of this arrangement, it is possible to provide, for instance, each semi-automatic opcrators position, one ccntrolling device, such as a keyboard.. and to provide a plurality of variably adjustable impulse sending or receiving' devices less in number than the operators positions.

A further feature or" the present invention contemplates the useo'r a controlling device at each of a plurality of operators positions, and impulse sending or recel" devices less in number than said opere-ta` positions and associable with any one of said plurality of positions., each of said impulse sending or receiving devices composed of a sender proper arranged to send or receive electrical impulses :tor the purpose of controllingthe operation of selector switchesAv and a registering dei ice associated with sain sender and variably' operable in accor y with the adjustment of any one of said controlling devices 'for the purpose et determining the operation of the sender, i

A still further featnre of this invention contemplates the use of a plurality of variably adjustable controlling devices, any one of which may be associated with any one of a plurality of variably operable imp sending or receiving devices, a garticu controlling device being associable with an idle one of the sending devices in response to the taking into use of a link or cord circuit.

Other features of the invention have to do with the arrangement of the controlling device by which the setting of the sending or receiving device may be determined by variations in the character of current, with the registering device which is responsive to currents of various character, such as low and high ipotential currents, with the arrangement of the sending or receiving device, the operation of which mayy be corrected by a so-called translating means, and with various other circuit combinations and arrangements, the character of which will be set forth in the following description of a preferred embodiment of the present invention and the appended .claims It will be obvious to those skilled in the art that the use of the present invention is not limited to the particular' type of switching and controlling devices disclosed, but is equally well applicable to systems in which no registering devices are interposed between the sender fand the operators keyboard and to systems in which the sender is of the directive rather than the revertiveimpulse type.

Figs. 1v to 11 of the drawings taken together illustrate diagrammatically a semimechanical telephone exchange system embodying the various fea-tures of the present invention. vThe order in which the drawings .should be considered is indicated in Fig. 12. Fig. 13 is a schematic showing of the arrangement ofthe terminals of the selectorV switches. This figure should be consulted when considering the translating system to be hereinafter set forth.

The reference numbers are used in the following manner: 1-99 in Fig. 11; 10G-199 in Figs. 1 and 9; 900-999 in Fig. 10; and in theother figures the hundreds digits of the numbers correspond to the number of the figure. For the sake of convenience, the name used in the description for designating certain switching devices is displayed in the drawings adjacent to the showing of such devices. SN and MG designate sensitive and marginal relays, and `H and L high and low wound resistances, yrespectively. Y

Selector sioz'czes.

The selector switches used in this system are of the soi-called power-driven panel type in United States Patent No.v

vdescribed 1,123,696 to E. B. Craft and J. N. Reynolds.` For 'the' purpose of distinguishing the various selector switches from each other, they will be hereinafter referred to in the following manner: District selector (Fig. 1), oliice selector (Fig. 9), incoming selector (Fig. 10), nal selector (Fig. 11), cord iinder, (Fig. 5) and sender selector (Fig. Each -of these selector switches has a vertically movable-brush rod carrying brushes arranged to wipe over a commutator plate, and thus control the operation of the respective selector switches, and wipers arranged to engage contacts of a terminal bank, by means of which connections may be established. With v the exception of the sender selector, which carries*l only one set of wipers, all the selectors referred to carry five sets of wipers. only one set of wipers being shown in the drawings. YThe terminal banks ofthe district, office, incoming and final selectors and of the cord finder, comprise 500 rows of terminals divided'into five sections, each of the sections comprising one hundred rows of terminals. Each set of wipers is arranged to engage any row of terminals Vin a certain section, but rests Vnormally. below the irst row of terminals of its respective section. The wipers of a set are normally held apart by means of a cam, whereby theyare out of the path of the terminals. By means of a tripping Vdevice associated with each of the selectors, any one of the wiper sets may be tripped .to move its wipers into the path of the terminals of its respective section. The tripping device of the district selector'and cord finder is of the same type as describedin United States Patent No.1,177-.Oa-r to J. L. McQuarrie, and the tripping device'shown in association with the. oihce, incoming and iinal selectors is of the type ldescribed in Vthe above mentioned Patent No. 1,123,696.

The difference between the two types of tripping device is that whereas, in the former, live magnets are arranged to control the tripping of certain wipers of anyone of a plurality of selector switches, in the latter each selectoris provided with one tripping magnet arranged to trip any one of its five sets ofwipers.

The brush rod of the sender selector ries a single set of'wipers which are always in a tripped position and rest normally on the Vlowermost row of terminals of a terminal bank. The wipersrof the lother selectors are tripped only when they are moved out of normal, but before they reach the lowermost terminals of their respective terminal sections.' Y

Seguence switches.

The sequence switches shown in this system are of the type described inUnited States Patentv No. 1,127,808.V Sequence switches 10S, 152, 913 and 10 control, by

iasV

figure. ln Fig. 2, two sequence switches 202 and 210 are indicated. Sequence switch 202 is the listening key sequence switch and controls the contacts shown below the horizontal dotted line in Fig. 2, and sequence switch 2l() is the key-control sequence switch controlling the contacts shown above the dotted line in this figure. Sequence switch 516 (Fig. 5) controls the circuits of the cord finder and the sender selector. All the sequence switch contacts shown in this lig'- ure, with the exception of those within the dotted rectangle, "are 'controlled by this sequence switch. The latter mentioned contacts are controlled by an allotter 583 ot the sequence switch type. Sequence switches 613 and 600 (Fig. 6) control, by means of their contacts shown to the left and right of the vertical dotted vline of this figure, the circuits or' a sender, and the circuits of aplurality of-registers, respectively. The sequence switch contacts shown in Fig. 7 are controlled by sequence switch 706. This sequence switch will be referred to as a. class register controller.

K 1/board).

The operators keyboard is shown in Figs. 3 and 4. lVhen, in any of the rows, a key is depressed, it is locked by mechanical means, which may be released in response to the cnergization of a magnet 342, one being provided for each row ot keys. There are nine rows ot' keys referred to as the office, tandem hundreds, tandem tens, tandem units, thousands, hundreds, tens, units and stations keys. Each row,with the exception of the oliice and stations keys, comprises keys numbered (l to 9, each key controlling` as many contacts as is necessary for controlling the selectors and -registers. 'The number ot oflice keys depends on the tra'ic requirements. The oti'ice keys are theequivalents oli' the tandem hundreds, tandem tens and tandem units keys; that isv to say, the depression ot one olliee key results in .the rsame combination ot impulses ast-he depression of a certain combinar on oi' tandem hundreds. tens and units ke One oHice key is provided for controlling ne seizure ot a trunk leading to an important ollice, whereas other oiTices may be reached by depressingr a prescribed combination of tandem keys.l

Registers.

'tations registers. lilith the exception ot e class and incoming group registers. each ister comprises three relays, two orn the i s being of marginal character :and one rush; 8, final tens; 9, iinal units; and l0,

Of the relays sensitive. The incoming group register comprises one sensitive and one marginal relay, and the class register, two sensitive and three marginal relays. Each 0f the register relays is provided with a locking winding, and depending on the combination in which thc relays ot a certain register are actuated, the operation ot the sender is determined.

' Sender.

The sender (Fig. 6) comprises a pair of wipers 635 and 636 arranged to be moved step-by-step over a circle ol' terminals in the direction indicated by the arrow, in response to each complete operation (energization and deenergization) of a magnet 634;. The terminals are divided into tour sections A, B, C and D. The terminals of sections A and B are connected to conductors 65T and 6&2, respectively. The five terminals oi sections C and D are numbered O to fi, and the terminals of these two sections designated by the same numerals are connected in multiple. The two terminals numbered 0 are interconnected by means of sequence switch springs 664 and 665 in certain positions of sequence switches 600 and 613. Magnet 6531i may be energized and deenergized under the control of a stepping relay 632. A relay 633 con.- trols the stopping oi the sender wipers in a certain position determined by the setting of the various registers. The numerals appearing in the circles at the contacts ot the various register relays indicate the terminal of the sender to which those contacts are connected.

Translation.

In the system disclosed, by means oi the district and oliice selectors, a ten-thousand line exchange may be selected. The called line terminating in this exchange is reached by the incoming and linal selectors. Each of the five sections ot' terminals in the terminal banks (Fig. 13) of the district and oiiice selectors is divided into .ten groups containing the terminals ot trunks leading to various oiiice and incoming selectors, respeetively. One group contains ten sets oi terminals. Each section of the incoming selcc tor is divided into four groups oi' terminals. each group containing twenty-five sets of terminals. Each section of the terminal bank of a final selector is divided into ten groups, each containing ten sets of terminals. For the purpose ot providing means for controlling the release of tie district, ot lice and incoming selectors. all the trunks of a group are busy, an overflow contact must be provided for each group ot trunks.

Each set or row of terminals in the terminal bank of the final selector serves as a calling terminal for a subscribers line. In the present case. it will be assumed that the linal selector, shown in Fig. l0, is one of a plurality of selectors that serves for seizing one of the lines numbered 9500 to 9999 (see also Fig. 13). The first section contains the terminals of lines 9500 to 9599, the second section 9600 to 9699, the third section, 9700 to 9799, the fourth section, 9800 to 9899, and the fifth section, -9900 to 9999.

Any one of the final selectors serving' these five hundred lines may be reached bymeans of any one of a plurality of incoming selectors. The trunks terminating in the various sections of the terminal bank of an incoming selector are numbered as follows: section No. 1, 0 to 1999; section No. 2, 2000 to 3999; section No. 3, 4000 to 5999; section No. 4, 6000 to 7999; and section No. 5, 8000, 9999. If the number of the desired line is 987 6, then it is necessary to trip the fifth set ofbrushes of the incoming selector, because this set of brushes serves the trunks terminating in the fifth section (8000 to 9999). The first group of trunks in this section leads to final selectors through which access may be had to subscribers lines numbered8000 to 8499, the secondv group of trunks leading to final selectors containing terminals numbered 8500 to 8999, the third group to final selectors through which access may be had to 9000 to 9499, and the fourth group contains trunks leading to final selectors through which ac'- cess may be had to subscribers lines 9500 to 9999. In the present case, it will be neces. sary to step the wipers of the incoming selector by four steps, and then operate it to select and seize an idle one of the trunks'leading to the final selector. All but the fifth set of wipers of the incoming selector are held out of thev path of the terminals of their respective sections. In the final selector, it will be necessary to trip the fourth set of wipers arranged to engage the terminals of the section 9800 to 9899, and the final wipers must then be stepped by eight steps, where` by the fourth set of wipers is positioned below the terminal No. 9870. By causing the final wipers to move seven steps the lterminal No. 9876 willbe'seized by the fourth set of Y wipers. v

The arrangement of the trunk terminals in the various sections of the terminal banks of the district and office selectors depends on trafiic'conditions, and in the present case, it will be assumed that the incoming selector shown in Fig.-10 is accessible in response to they depression of the B office key controlling the 'tripping of the second set of wipers of the district selector, the stepping of these wipers onto the ninth group of terminals in the second section ofthe terminal bank and then the tripping of the fourth set of wipers of the ofiice selector, and the setting of these wipers onto thesecond -group of terminals in the fourth section of the terminalbank of the oflice selector. Y v

In view of the fact that the'numerical designations of the terminals of sections C and D of the sender are identical, and that the various registers may control theV sender to stop in one out of five positions, means must be provided forv causing the sending of additional impulses if kthe selector must be stepped by nine steps, as in the case of the district selector, or generally if it is desired to send more than five selective impulses. This is done by providing translating relays, such as 742 and 721 (Fig. 7 ),v and 832 and 821 (Fig. 8). merical designation of the v key actuated,

Depending on the nu- Y these translating relays are operated to de- Y termine on which of the two terminals (1 1, or 2 2, etc) the sender wiper 635 should stop; that is to say, if it is desired to step the wipers of the districtselector by nine steps, then the Vdistrict group reigster relays are set so as to close a circuit forrelay 633 when the sender wiper 635 has been moved by four steps, and reaches terminal No. 3 in section C. In order to cause this wiper 635 to step onto terminal No. 3 in section D of the terminal bank of the sender and thus take nine steps fromits normal position, relay 721 is energizedrso as to insure the taking of fiveV additional steps by the sender wipers. If relay l742 is energized, then the sender takes five additional steps when the office group impulses are sent. If relay 832 is energized, the sender takes five additional steps when the final tens impulses are sent, and in response to the energization of relay 821, thesender is caused to take five additional steps when the final units impulses are sent. In view of the fact that a section of the terminal bank of the incoming selector is divided into four groups, it isY not necessary to provide translating means for controlling the sending of incoming group impulses. Y

Brief outline of operation.V

A subscriber at station 100 (Fig. 1), desiring to obtaina connection with a subscriber at station 33 (Fig. 1,1) located in a dista-nt semi-mechanical exchange causes theiactuation of a signal CL atan operators position. The operator extends the calling line by an idle one of a plurality of cord or trunk circuits such as 105, provided at her position, one end of this cord terminating-in an answering plug 101, and the other in the wipers of the district selector.

In response to the extension ofthe calling line, the listening key sequence switch 202 individual to the cord 105 taken into use, associates the operators telephone set 200, common to a plurality of cords, withV the 'cord 105. VThere are a plurality vof cord finders and sender selectors similar to those shown 1n Fig. 5.

tor service. As soon as the sequence switch 108 moves into position 2, the preselected cord linder and the associated sender selector, the sequence switch 516 of which is in position 1, are started. The cord inder hunts tor terminals representing the cord 105, and when these are reached, the cord finder is stopped. The sender selector limits tor an idle one of a plurality of senders. The relay arrangement shown within the dotted rectangle in the lower right-hand portion of Fig. 5, is provided in common for a plurality of cord inders and operates to prevent the tripping of' a plurality of brushes on a cord finder if a plurality et sequence switches like 10S are moved simultaneously into position 2. The arrangement shown within the dotted rectangle in the lower left-hand portion of Fig. 5, is individual to a group of cord circuits 105 and controls the operation of the arrangement in the lower right-hand portion oit Fig. 5, and may prevent the operation thereof it only one call is coming in at a time, and thus there is no danger ot two sets or" cord finder wipers being tripped.

At each operators position there is provided one keyboard with its associated controlling apparatus, shown in the upper portion oi' Fig. 2 and in Figs. 3 and 1. In response to the movement of any one of the listening key sequence switches provided at an operators position into the listening-in position (7) and the movement ot the sequence switch 108 into position 2, the operators keyboard is seized for use; that is to say, operatively associated with the sending and registering arrangement shown in Figs. 7, G and 8 through the cord finder and sender selector,

TheV operator then depresses the keys designating the number of the called line. It the called subscriber is located in a semimechanical exchange that may be reached in response to the `depression of the oiiice key B, the operator does not depress any of the tandem keys, neither does she depress a stations key. Assuming that the called subscrihers number is B-9876, the operator depresses the ilo. B oiiice, No. 9 thousands, the No. 8 hundreds, No. T tens, No. 6 units, and the start key 114. The depression of the oliice key results in the energization of certain of the relays shown in Fig. 3. These relays may also be controlled to operate in a certain combination in response to the depression oi the tandem keys. As a result of the actuation of acertain combination of the mentioned relays and due to the particular wiring of the thousands. hundreds, tens and units keys` the operations of the marginal relays of the registers and that of the translating relays are determined. Certain ot the marginal register relays may he prevented or permitted to operate by connecting the low i'esiStaI-lees 319 or 339 or the high resistances or 327, in series with such relays, or by completing or not completing the circuit of these relays through certain key contacts during the setting of the registers. The other marginal register relays are energized or left deenergized depending on the insertion oit hoth windings of relays 220 and 238, or only the low resistance left-hand windings of these relays in series with such relays.

The depression of the otlice key B causes the tripping of the second set of wipers ot the district selector, the setting of the class and district group registers, the energization of relay 721, and the setting ol' the othce brush and ollice group registers. The shitting of the control of the oiiice key B from one register to the other is accomplished by the key control sequence switch 210 and the register control sequence switch 600. vIn position 2 of these sequence switches, the class register is set; in position 3, the district group register; in position t, the office translation is controlled; in position 5, the otlice brush register is set; and in position 6, the office group register is set.

The setting of the class register depends on the character of the connection desired. In the present case, when a semi-mechanical connection is desired, the class register is left in position l and exercises a certain control on the operation ot the system to be set forth during the detailed description ot the operation of the system.

After the setting of the onice group register, the sequence switches 210 and 600 remain in position 7 until moved into position 8, the former in response to the depression of the start key, and the latter under the control of class register sequence switch 706. It the class register sequence switch 706 is lett in position l, the sequence switch 600 is moved into position 8 for permitting the setting of the incoming brush register under the control. of the depressed thousands key. It another type of connection is desired, then the class register is moved out of its normal position and moved into another position than 8.

The depressed thousands key causes also the setting of the incoming group register in position 9 of sequence switches 2,10 and 000, in cooperation with the depressed hundreds keys. The actuated hundreds key controls in position 10 ot sequence switches 210 and G00, the setting of the final brush register.

The operated tens key causes in position 11 ot sequence switches 210 and 600 the setting of the tens register, and in position 12 of these sequence switches, under the control ot the depressed tens and units keys, the relays 832 and 821 are energized if translation is desired,

The units key controls the setting et the units register in position 13 of sequence switches 210 and 600.

In position 14 of the sequence switches 210 and 600, the `stations register is set under the control ot a start key 416, but in view or' the'itact that in a semi-mechanical sender wiper 635 engages terminal No. 2, it

all the three register relays are deenergized; when wiper 635 engages terminal No. 3, it relays 812 and 811 are deenergized and relay 81d is energized; and when the sender wiper'engages terminal No. e, it relay 812 is energized and relays 811 and 81% are deenergized. The relays of the other registers control the stopping oi the sender in a similar manner. rJhe incoming group register, however, controls the stopping of the sender with wiper 635 on terminal No. 3 when the sensitive and marginal relays are deenergized; on terminal No. 2, when the sensitive relay is deener'gized and the marginal relay energized; on terminal No. 1, when the sen- Cil sitive relay is energized and the marginal relay deenergized; and on terminal No. O when both relays are energized.

After the setting ot' the class, district group, otiice brush and office group registers and in position 2 ot' sequence switch 613, the district selector is operated and sends `impulses over a fundamental circuit to operate the magnet'63- through the .agency oit ai,

sender stepping relay 632. After the wipers have been stepped by nine steps, the relay 633 becomes cncrgilzed, opens the t'undainental circuit, causes the restoration of the sender and the advance of sequence switch 613. During the restoration ot the sender the district selector automatically selects an idle trunk leading to the ol'lice selector. In position /lot the sequence switch 613, tour impulses are received by the sender under the control or the olliee selector, und in accordance with the setting ot' the oiice brush register. After the receipt of the :tour impulses the relay 633 operates inY the above described manner and advances the sequence switch 613 into position 6.

Two ottice group impulses are received from the oiiice selector in accordance with the setting ot the otlice group register and the relay 633 operates to advance the sequence Amoved into position 18.

switch 613 into position 8. In positions 8, 10 and 12 of the sequence switch 613the tandem hundreds, tandem tens, and tandemY units impulses may be sent'out. In view of the tact that, in the present case, the sending of such impulses is not desired, due to the setting of class register sequence switch 706, the sequence switch 613 is advanced from position 7 into position 111. In the meantime, the oiiice selector selected an lidle trunk leading to the incoming selector.

After the registers shown in F ig. 8 have been set, the incoming selector Vsends tive impulses into the sender inv accordance with the setting of the incoming brush register, whereupon the sequence switch 613 is advanced to position 16 in the above described manner, for receiving the group impulses in accordance with the setting of the group register under the control of the incoming selector, whereupon sequence switch 613 is The incoming selector hunts for an idle trunk in the selected group. Then the sender receives four impulses from the final selector in accordance with Vthe setting of `a final brush register, whereupon the sequence switch 613 is moved again into position 2, but, due to the fact that the sequence switch 600 was moved in the meantime into position 16, the sender receives now the iinal tens impulses instead ot the districtgroup impulses. After the receipt of eight impulses under the control of the final selector, the sequence switch 613 is moved intol position 4 and'receives now, instead' of the oihce brush impulses, the iinal units impulses under the control of the final selector. The sender sequence switch 613 is moved then into position 6, but, underthe control of class register sequence switch the sending of stations impulses is prevented. The sender, the registers, the sender selector, the cord finder, and the keyboard Y are then released to normal and ready for controlling the setting up of another connection.

Y Detailed description line relay LR becomes energized and causes the lighting of acalling lamp CL. An operator, whose head set is indicated at 200,'

vinserts thereupon a plug 101 into an answering jack .102 in which the calling subscribers line terminates. A circuit is closed thereupon from grounded battery, through the winding of a cut-otfjrelay CO, the'sleeve contacts of jaclr'lOQ and plug 101 and the winding of relay 103 to ground, and another circuit trom the plus pole ot battery, through the primary winding of a repeating coil 104C, the winding 'of an answering supercontacts of jack 102 and plug 101, the ripper limb of cord circuit 105 and the primary winding of repeating coil 1011 to the minus pole of battery.V Relays CO, 103 and SR bccome energized. The relay CO disconnects relay LR', whereupon lamp CL becomes extinguished.

Relay 103 closes a circuit from ground, through its armature and front contact, conductor 106, the lower right-hand contact of sequence switch spring 201 and the power magnet of sequence switch 202 to grounded battery. Under the control of its normal contact 203, the sequence switch 202 is moved out of position 1 and into position 7. ln position 7 of the sequence switch 202, the operators telephone set 200 is connected lby means of sequence switch contacts 204 and 205 to the cord circuit 105, and thus the operator is enabled to converse with the calling subscriber. When the sequence switch 202 reaches position 7, a circuit is closed from ground, through sequence switch contact 206, a conductor 207, the upper righthand contact of sequence switch spring 107, and the power magnet of sequence switch 108 to grounded battery. Sequence switch 108 is moved out of position 1, and under the control of its normal contact 109. into position 2. Another circuit is closed from ground, through sequence switch contact 208, contact 209 of sequence switch 210 and the winding of a relay 211, to grounded battery. Relay 211 becomes energized and closes a locking circuit for itself through its right-hand front contact and armature and sequence switch contact 208.

As indicated in Fig. 2 ot the drawings, the relay 211 is common to a plurality of listening-key sequence switches and thus it may be energized also in response to the closure of a sequence switch contact 208 controlled by another listening-key sequence switch of the operator.

Sett/ag of the cord finder zml the Sender selector.

Assuming that several. cord circuits are simultaneously taken into use by various operators, and thus Several sequence switches like 108 are in position 2, a circuit is closed from ground, through the lower right-hand contact of sequence switch spring 112. conduct-or 111 (Figs. 1, 2 and 5), the lower armature and back contact of a relay 500, the lower armature and back contact of a relay 501, a resistance 502 and the winding of a marginal relay 503 to grounded battery. A similar circuit is closed for the relay 503 by each ot the sequence switches corresponding to 108. Each ot these circuits includes a resistance like 502 and, for this reason, the

, energized.

relay 503, which is marginal in operation, is operated. Relays 500 and 501, resistance 502 and the conductors shown in the lower left-hand corner of Fig. 5, are individual to the-link circuits 105 ot' the operators position. Similar apparatus are individual to each of the other positions. Relay 503 closes a circuit from ground, through its armature and front contact, the armature and back contact of a relay 504C, and the back contact and armature of a magnet 505 to grounded battery. Magnet 505 interrupts its own circuit and thus causes, by means ot a pawl 506 fixed to its arniature,the stepping of wipers 507 and 508 mounted on a ratchet wheel 509. The wipers l)07 and 508 are arranged to traverse terminals representing groups of link circuits. As soon as the wiper 508 engages terminal 510 indiyidual to the group in which the link circuit 105 belongs, a circuit is closed 'from grounded battery, through the winding or relay 504C, wiper 508, Vterminal 510, the lower back contact and armature ot relay 501, the lower back Contact and armature ot relay 500, conductor 111 and sequence switch contact 112 to ground. Relay 501 becomes energized and opens in its back contact the operating circuit of magnet 505, whereupon the wipers are arrested. Relay 5011- closes also a circuit from ground, through the armature and front contact oi relay 503, its armature and .trent contact, the armature and back contact ot' a relay 511, and the lett-hand winding ot a relay 512 to grounded battery. Relay 512 closes a locking circuit for itseltl from ground 518 individual to the group ot cords 105,

the lower winding of relay 501, and the windings ot relays 511 and 511` to grounded battery. Relays 511, 5141 and 501 become lVhen relay 501 opens in its lower back contact the energizing circuit ot relay 503. this relay is maintained energized by a circuit closed through the lower back contact of another relay 501 individual to 'another group of calling link circuits. Re-

lay 501 becomes deenergized. Relay 511 closes a circuit from ground through its armature and tront Contact. the upper letthand contact ot sequence switch spring 515, and the left-hand winding ot' a relay 517 to grounded battery. As will he hei-ei after set forth, only one sequeni'fe switch like 510 is in position 1 at a time, and for this` reason the energization of relay 511 results in the energization of only one relay like 517.

Upon the energization of relay 501 a circuit is closed from ground. through the lower ri gilt-hand contact ot sequence switch spring 112, conductor 111. the lower armature and back contact and the lower armature and Vtrent contact et relays 500 and 501 llO - wipers similar to 533.

carried by cam 535.

respectively, and the winding of a trip magnet 541 to grounded battery.- YThe trip magnet 541, by attracting its armature, moves a trip finger 542 into the path of a catch 543 The connection of ground to the lower front contact of relay 501 results also in the shunting out of relay 512, which thereupon becomes deenergized. Before the wipers of set 533 engage the lowermost terminals of bank 534 as will be hereinafter set forth, the trip finger actuates catch 543, causing thus cam 535 to be removed from between the wipers; whereupon these wipers are permitted to move in alignment with the terminals of the bank.

Upon the dcenergization of relay 504, relay 503 causes magnet 505 to move the wipers 507 and 508 away from terminals 513 and 510. Relay 504 breaks the circuit of magnet 505 in the same manner as above described when wiper 508 linds the terminal individual to the group containing the next calling link circuit.

The wipers of the sender selector 518 are normally resting on a set of contacts in which conductors leading to a sender terminate. Supposing that this sender is busy, as

will be hereinafter set forth, ground is connected to terminal 519. For this reason a locking' circuit is closed for relay 517, through wiper 520 of the sender selector 518, and the right-hand armature, front contact and winding, of the relay 517. Upon the energization of relay 517, a circuit is closed from ground, through the left-handk armature and front contact of thisrelay, the upper right-hand contact of sequence switch spring 521 and the winding of a relay 522 to grounded battery. Relay 522 closes a circuit from ground, through its right-hand armature and front Contact, the

lower left-hand contact of sequence switch spring 523 and the power magnet of sequence switch 516 to grounded battery. The sequence switch 516 is thereupon moved Yout of position 1, and under the control of its normal spring 524, into position 2. A circuit is now closed from grounded battery, through the winding of a magnet 525, the upper contacts of sequence switch spring 526 and the right-hand front contact and armature of relay 522 to ground, and another circuit from ground, through the left-hand armature and front contact of relay 517, the upper left-hand and lower right-hand contacts of sequence switch spring 527, and the winding of amagnet 529 to grounded battery. Magnets 525 and 529 become energized. By attracting its armature magnet 525 presses brush rod 530` of cord finder 531 against a roller 532 constantly rotating in the direction indicated by the arrow. The brush rod 530 carries a plurality of sets of These wipers are arranged to engage the sections of the terthe wipers of each set are normally heldV apart by means of a cani like 535. A brush 536, arranged to engage various segmentsV of a commutatorplate isalso carried by brush rod 530. As soon as the brush rod hasbeen moved in'an upward direction far enough to permit brush- 536to engage conducting segment 537, which happens prior to the engagement by the wipers 533 of the lowest row'of terminals of the respective bank section, a circuit is closed Vfrom ground, through brush 536, conducting plate 537, the right-hand contacts of sequence switch spring 560, the upper front contact and armature of relay 501, and the uf'inding of relay 500y to grounded battery. The relay 500 becomes energized and closes a locking circuit for itself through conductor 111 and sequence switch spring 112, to ground, whereupon relays 501, 511 and 514 become deenergized. VRelay 514 closes a circuit from ground, fthrough its armature and back contact, the upper right-hand contact of sequence switch spring 523, and the power magnet of sequence switch 516, to grounded battery, whereupon the sequence switch is moved out of position2 and into position 3. Relay 511 being deenergized,

the relay 512 is permitted ,to operate under the control of the next calling cord circuit.

Vhen the sequence switch- 516 moved out of position 2, relay 522 Ywas maintained energized by a circuit extendingv fromvground, through its winding, the upperA left-hand contact of sequence switch spring 521, and the right-hand back contact and armature of a test relay 545 to ground. As soon as the wipers 533 engage the'rset of terminals representing cord A105, a circuit is closed from ground, through the upper right-hand contact Yof sequence switch spring 112, a conductor 186, a resistance V21.2, conductor 213, terminal V546, wiper ,574,v the lower right-hand contact of sequence Vswitch spring 547, and the windings of relay 545 to grounded battery. If full battery potential exists on terminal 546; that is to say, if no other cord linder engages with its test wiper this terminal, then relay 4545, which is marginal in operation, becomesV energized vided in the right-hand armatureY and frontV contact of relay 545, anda resistance 548, for decreasing the potential on test termi- 

